[dsd] Support container-level UDP origin detection

[ahmed-mez]

What does this PR do?

Extend origin detection on UDP by supporting tagger-ready origin strings in dd.internal.prefixed_origin.

Motivation

• More granular tags (container tags instead of pod tags)
• Not limited to Kubernetes, and can be a good alternative in environments where origin detection on UDS is not an option (e.g Fargate)

Additional Notes

Client side logic is implemented in DataDog/datadog-go#250

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

Deploy the agent with DD_DOGSTATSD_ORIGIN_DETECTION enabled

echo -n "testing.dsd.container:1|g|#foo:bar,dd.internal.prefixed_origin:container_id://<your container ID>" | nc -u -w1 <Agent IP> 8125

You should be able to see container tags attached to the testing.dsd.container metric on the app.

Reviewer's Checklist

• If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
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• Use the major_change label if your change either has a major impact on the code base, is impacting multiple teams or is changing important well-established internals of the Agent. This label will be use during QA to make sure each team pay extra attention to the changed behavior. For any customer facing change use a releasenote.
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• Changed code has automated tests for its functionality.
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• If applicable, docs team has been notified or an issue has been opened on the documentation repo.
• If applicable, the need-change/operator and need-change/helm labels have been applied.
• If applicable, the config template has been updated.